universiti teknikal malaysia melakaeprints.utem.edu.my/16352/1/springback effect on various...
Post on 23-Aug-2019
213 Views
Preview:
TRANSCRIPT
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
SPRINGBACK EFFECT ON VARIOUS THICKNESS OF MILD
STEEL, STAINLESS STEEL AND ALUMINIUM SHEET.
This report submitted in accordance with requirement of the Universiti Teknikal
Malaysia Melaka (UTeM) for the Bachelor Degree of Manufacturing Engineering
(Manufacturing Process) with Honours.
by
SARIFUDDIN BIN MOHD AMIRULLAH
B051110310
910930-12-6041
FACULTY OF MANUFACTURING ENGINEERING
2015
APPROVAL
This report is submitted to the Faculty of Manufacturing Engineering of UTeM
as a partial fulfillment of the requirements for the degree of Bachelor of
Manufacturing Engineering (Manufacturing Process) (Hons.). The member of
the supervisory is as follow:
(Signature of Supervisor)
………………………….
(Official stamp of Supervisor)
(Signature of Co-Supervisor)
……………………………..
(Official stamp of Co-Supervisor)
i
DECLARATION
I hereby, declared this report entitled “Springback Effect on Various Thickness of
Mild Steel, Stainless Steel and Aluminium Sheet ” is the results of my own
research except as cited in the references.
Signature : ………………………………………….
Author’s Name : Sarifuddin Bin Mohd Amirullah
Date : …………………………………………
ii
DEDICATION
Special thanks, I dedicated to my beloved family, especially to my mother,
Khadijah Dualis Binti Abdullah for their advices and continuous support to me in
performing this difficult task and journey does not end here. Special dedicated to
my supervisor, Mohd Fairuz bin Dimin @ Mohd. Amin and to all my fellow
friends. This project is completed and achieved cannot be done without all of you.
iii
ACKNOWLEDGEMENT
Praise to Allah the Almighty for giving me the strength and patience to finish my
Final Year Project Report.
I would like to take this opportunity to express my sincere and deepest gratitude to
my Project Supervisor, Mohd Fairuz bin Dimin @ Mohd. Amin for his guidance and
feedback provided to me during the final year project process. The greatest thanks to
my beloved family for their prayers and support to me throughout this entire period
of this Final Year Project 1 and 2. I would like to convey my biggest thanks to all
FKP technicians for supporting me throughout my project.
I especially would like to thank my mother for her support and encouragement.
Without their prayers continuous encouragement and moral support, this study would
not be possible to complete.
I am also obliged to everyone who had directly and indirectly involve through
contributions of ideas, as well as materials and professional opinions. Without
anybody, I cannot achieve what I have done with the final year report. Last but not
least, I would like to thank everyone who directly or indirectly involved through the
contribution of ideas and materials as well as professional opinions to this project
had been successfully done.
iv
ABSTRACT
The purpose of this research is to conduct an experimental study springback effect
and thinning effect on various thickness of Mild Steel, Stainless Steel 304 and
Aluminium Alloy 6061 Sheet. The springback effect is measured on with a different
thickness for Stainless Steel 304, Mild steel, and Aluminium Alloy 6061. The
thinning effect also measured by using a different thickness for Stainless Steel 304,
Mild steel, and Aluminium Alloy 6061. The optimization value for each response,
springback and thinning effect is obtained through optimization model in Minitab 17
software. For springback effect, optimize setting is gained by using Aluminium
Alloy 6061 with a thickness of 1mm. At the same time, the optimize setting for
thinning effect is by using a Stainless Steel 304 with a thickness of 1mm. The
springback and thinning effect are measured and the analysis Multi Regression
analysis is conducted. By using an analysis tool in Minitab 17, the relationship
between the variables and responses can be obtained. The result showed the variables
which are thicknesses and materials and the responses which is springback and
thinning effect are statistically significant. The p-value for springback effect is equal
to 0.002. While, R-squared value obtained for springback effect is equal to 93.56%.
For thinning effect, the p-value is less than 0.001 and the R-squared value computed
is equal to 99.63%.
v
ABSTRAK
Tujuan kajian ini adalah untuk menjalankan eksperimen tentang pengaruh
springback dan kesan thinning terhadap pelbagai ketebalan bahan seperti keluli
lembut, keluli tahan karat 304, dan kepingan Aluminium Alloy 6061. Kesan
springback dinilai melalui 3 jenis bahan iaitu keluli lembut, keluli tahan karat 304,
dan kepingan aluminium alloy 6061 dengan setiap bahan mempunyai 3 ketebalan
yang berbeza. Kesan thinning juga dinilai dengan menggunakan cara yang sama
untuk menilai kesan springback.Nilai pengoptimuman untuk setiap respon,
springback dan kesan thinning diperolehi dengan menggunakan perisian Minitab 17.
Untuk kesan springback, aturan optimum yang diperolehi adalah dengan
menggunakan kepingan Aluminium Alloy 6061 dengan ketebalan 1mm. manakal
untuk kesan thinning,aturan optimum diperolehi adalah dengan menggunakan keluli
tahan karat 304 dengan menggunakan ketebalan 1mm. springback dan kesan
thinning dinilai dan analisa Multi Regression dijalankan. Dengan menggunakan
perisian Minitab 17, perhubungan di antara pembolehubah dan respon boleh
diperolehi. Keputusan yang diperolehi menunjukkan pembolehubah seperti ketebalan
dan jenis bahan dengan respon seperti springback dan kesan thinning mempunyai
perhubungan statistik yang signifikan. Nilai p untuk kesan springback bersamaan
dengan 0.002. Manakala, nilai R-kuasa dua diperolehi adalah bersamaan dengan
93.65%. Unuk kesan thinning, nilai p adalah kurang daripada 0.001 dan R-kuasa dua
didapati adalah bersamaan dengan 99.63%.
vi
TABLE OF CONTENT
Approval i
Declaration ii
Dedication iii
Acknowledgement iv
Abstract v
Abstrak vi
Table of Content vii
List of Tables ix
List of Figures x
CHAPTER 1: INTRODUCTION 1
1.1 Overview of Study 1
1.2 Background 1
1.3 Problem statement 3
1.4 Objective 4
1.5 Scope of Study 4
CHAPTER 2: LITERATURE REVIEW 5
2.1 The Sheet Metal. 5
2.2 Springback Effect and Thinning Effect. 6
2.3 Springback Effect and Thinning Effect on Various thickness. 9
2.4 How to Optimize Springback and Thinning Effect. 10
2.5 Design of Experiment. 16
2.5.1 Factorial Experiments. 16
vii
CHAPTER 3: METHODOLOGY 18
3.1 Introduction to Methodology. 18
3.2 Planning of Study. 20
3.3 Research Process Flowchart 23
3.4 Experiment. 24
3.4.1 Equipment. 24
3.4.2 Material Properties for Each Material. 25
3.4.3 Procedure. 26
3.5 Experimental Design. 27
3.6 Data Collection. 27
CHAPTER 4: RESULT AND DISCUSSION 28
4.1 Springback Result 28
4.1.1 Springback effect analysis on Stainless Steel 304, Mild
steel, and Aluminium Alloy 6061 in different thickness
29
4.1.2 Optimization of Springback effect on Stainless Steel 304,
Mild Steel, and Aluminium Alloy 6061 in different
thicknesses.
31
4.2 Thinning Effect Result. 32
4.2.1 Thinning effect analysis on Stainless Steel 304, Mild
steel, and Aluminium Alloy 6061 in different thicknesses 33
4.2.2 Optimization of Springback effect on Stainless Steel 304,
Mild steel, and Aluminium Alloy 6061 in different
thicknesses. 34
CHAPTER 5 CONCLUSIONS AND RECOMMENDATIONS 35
5.1 Conclusions. 35
5.2 Recommendations. 36
REFERENCES 37
APPENDICES 40
viii
LIST OF TABLES
3.1 Gant chart for PSM 1 21
3.2 Gant chart for PSM 2 22
3.3 List of equipment used. 24
3.4 Material properties of Stainless Steel 304. 25
3.5 Material properties of Mild Steel. 25
3.6 Material properties of Aluminium Alloy 6061. 25
3.7 Samples thickness and dimension. 26
4.1 The result of the Springback. 28
4.2 The final equation generate by the Optimization
model for Springback. 31
4.3 Solutions for optimization of Springback. 31
4.4 The result of the Thinning effect. 32
4.5 The final equation generate by the
Optimization model for Thinning effect. 34
4.6 Solutions for optimization of Thinning effect. 34
ix
LIST OF FIGURES
1.1 Definition of Die Parameters 3
2.1 Process Steps During Bending And Springback 10
2.2 Methods Of Springback Control In Bending 12
2.3 Gap Between Forming Punch And Die 12
2.4 Schematic Of Overbending To Compensate for
Springback in bending 13
2.5 Schematic Of Overforming To Compensate for
Springback In The Bottom Of The Channel 14
2.6 Channel Cross-Sectional Design For advanced high -
Strength steel with larger included angles to facilitate
manufacturing 14
3.1 Flow chart of activity in PSM 23
3.2 The shape of the sample with 3 different thicknesses 27
4.1 The comparison of Springback between materials and
thicknesses 29
4.2 The p-value and R-squared value for Springback effect 30
4.3 The comparison of Thinning effect between materials
And thicknesses 32
4.4 The p-value and R-squared value for thinning effect 33
x
1.1 Overview of study
This report issue associated with the springback effect on various thickness of
Stainless Steel 304, Mild steel, and Aluminium Alloy 6061. In this report, the
influence of thicknesses of sample onto springback effect and thinning effect is
conducted .
1.2 Background
In early of 1958, the springback corrections’ generalized mathematical analysis in
the metals pure bending for example, aluminium, nickel, ferrous alloys, and titanium.
Johnson and Yu (1982) conducted a research to produce springback’s theoretical
analysis for the elastic–plastic, rectangular plate’s bi-axial pure bending. Ayres
(1984) suggested a process named “shape-set” with a purpose to decrease side-wall
curl springback that always happen to high-strength steel (HSS) rails. Prasad and
Somasundaram (1993) created a plane-strain sheet bending models with a reason to
foresee the springback, minimum value of bending ratio, bendability, maximum
forces on the punch and the die, and the strain and stress distributions. The empirical
methods to calculate the bend allowance is evaluated by them. They also developed
and created a mathematical model to identify the bend allowance according on the
INTRODUCTION
CHAPTER 1
1
properties of material for example, the tool geometry and the strain-hardening
exponent and yield stress of the material. Leu (1997) analyzed The Hill’s theory in
anisotropic materials and he had proposed an equations with a purpose to calculate
the springback and bendability in plactic bending based on anisotropic sheet metals.
It is hard to gain very detailed and accurate outcomes in metal forming, arisw from
the variables and the forming conditions of the sheet metal when using a traditional
analytical methods.
Noordalila (2011) stated that springback is a simply the total of the strain returned to
the part as the stress returns to zero. It can be estimated with this formula:
esb=S/E 1.1
where;
esb = Springback.
S = Forming stress.
E = Elasticity Modulus.
while the forming stress at any point is not easy to determine, the usage of proxy
stress can be used to determine the forming stress. It can ease to understand by
simplifying the forming stress (S) by assumption that all parts must in condition
where the parts is stressed beyond their yield point:
S ≥ YS, therefore, esb= YS/E
Where;
Y = Yield point.
2
Figure 1.1: Definition of die parameters. (Leu, 1997)
1.3 Problem Statement
Bending process is one of the common process used in industry such as
automotive industry, construction industry and others industries. However the
accuracy and desired geometry the sample of is influence by the springback effect
and thinning effect. There is a lot factors that influence the springback effect and
thinning effect usch as thicknesses of sample, material properties, die’s radius, die’s
clearance, ratio of bend radius to sheet thickness, and anisotropy of the material and
others factors. Nevertheless, the thickness of the sample and the type of material
provides a greater effect on the accuracy of this process. Will various thickness of
this three type of material which is Stainless Steel304, Mild steel and Aluminium
Alloy 6061 affect the springback effect and thinning effect? To gain complete
information on this matter, a research is proposed and conducted.
3
1.4 Objective
1. To measure the thinning effect during bending process with a different thickness
for Stainless Steel 304, Mild steel, and Aluminium Alloy 6061.
2. To measure the springback effect during bending process with a different
thickness Stainless Steel 304, Mild steel, and Aluminium Alloy 6061.
3. Optimization of springback effect and thinning effect by manipulation of
thickness on Stainless Steel 304, Mild steel, and Aluminium Alloy 6061.
1.5 Scope of Study
This research focus on the one of the parameter that greatly influence the
springback effect and thinning effect which is the thickness of the sample on three
type of material which is Stainless Steel 304, Mild steel, and Aluminium Alloy
6061. The three different materials used in this experiment is to investigate the
relationships between the springback and thinning effect. The material properties of
the samples are also one of the parameter that influences the springback and thinning
effect. The research will provide a great information regarding to the springback
effect and thinning effect on a various thickness for three type of material that have
been stated. However, the research is conducted by bending the materials into 90°
and no other way involve in this research. The springback effect and thinning effect
on various thickness for a different shape is not available. The mould and the radius
of the die is fixed and unchangeable.
4
This literature review will discuss in detail on the issue about the reviews from
previous researches that is related with the step approach for identify the springback
effect on various thickness of steel, stainless steel and aluminium sheet. This chapter
is included explanation about the related study based on this project.
2.1 The Sheet Metal
Sheet metal is a flat, and thin pieces formed by an industrial processes. In
metalworking, this form is very important because it can be bent and cut into a many
type of shapes. Objects that have been used in everyday life are composed with sheet
metal. The thicknesses can be differ significantly, leaf or foil is an extremely thin and
plate is and a piece that thicker than 6mm are treated as a plate. The sheet metal can
be found in coiled strips or flat pieces. The coils are formed by continuously running
a set of length of sheet metal through a roll slitter. There are various types of metals
can be formed to sheet metal, such as brass, aluminium, nickel, tin, steel, titanium
and copper. For aesthetic function, significant sheet metals such as platinum, silver,
and gold. Sheet metal made of platinum can be used as a catalyst. Application of
sheet metal is vary from airplane wings, car bodies, roofs for buildings, table for
medical purposes and other applications (Lodhi & Jain, 2014).
LITERATURE REVIEW
CHAPTER 2
5
2.2 Springback Effect and Thinning Effect.
Spring back effect always haunted a sheet metal forming industry. The springback
effect is an undesired form of metal after unloading phase lead to the unwanted
dimension. Springback phenomenon occurs because of the elasticity of the bent
material. Wagoner, Lim, & Lee (2013) said nowadays, springback is known as a
change in shape which is driven elastically that happens following in operation of
sheet forming when the forming loads which holding and reshape the work piecec
are withdrawn from the work piece. Usually this event is undesireable, lead to the
problems for example the tolerances is increased and the variability in the sequence
forming operations, in fabrication and assembly, and in the concluding part.
Typically, this effects downgrade the quality and appearance of manufactured
products. Papadakis (2008) state that the definition of Springback is the driven
alteration in shape of a component part upon unloading after forming. This problem
is increase as have a tendency to progressively rely on upon materials with higher
strength-to-modulus ratios compare to the traditional low-strength steel. Mostly in
FE-codes for sheet metal forming simulation, the strain recovery is assume to be
linear and elastic, and the code do not weight out the the inelastic effects occur
during calculation of springback.
Burchitz (2008) stated springback as an phenomenon driven elastically that change
the shape of the part being deformed upon removal of the loads. This phenomenon
caused the the deviation of the geometry of the real product from the desired design
and resulted a significant problem in process of assembly. It is a phenomenon with a
complex physical which is mainly due to the stress state gained after the deformation
process.
While Smith (2005) said springback happen after a trim, flanging, and draw on the
panel caused by the unbalanced residual stresses. The geometry of the panel is
deviate from the desired shape caused by the after effect of springback. The previous
definition supported by Duhovnik, Demšar & Drešar (2014) stated the sheet-metal
thickness affect the bend radius in the sense that it takes account of a certain factor
(e.g., 0.8-2.0 x d). The most common ratio used is 1.0, for example, the thickness of
sheet-metal same as the bend radius of the sheet metal after deforming. Bending
6
forces are rapidly increasing, especially the residual stress in a material because of
the deformations of plastic when a small radius of die is used. It causes increased
return deformations after bending—the so-called “spring-back” effect. Resetting
certain features can be done.
The definition given by Indian Space Research Organisation Antenna Systems Group
(2005) said that the shaping a structure of laminated composite in contact with the
mould involves distortion of geometric on the structure, which is commonly called as
reverse springback or spring-in. Jin & Lin (2012) stated that any types deformation
of plastic on the sheet metal under outside loads comprise of the elastic deformation
and deformation of plastic. When the external loading is removed, parts are deform
induced by the plastic deformation of materials that memorise the residual
deformation. However, the sizes of the deformation is shifted in the opposite
direction after the load changes caused by the elastic deformation, plastic
deformation and elastic recovery of elastic deformation part of the elastic recovery of
its shape, this event is called as springback, which likely happen in all types of the
stamping process. Categorically in order with the non-conventional forming
stamping, and sheet metal bonding forming involved bulging, flanging, bending,
local shape, flaring, bending, and necking, etc. The most familiar in in the bending
process is the springback after unloading is the most crucial.
Lemeš (2010) stated springback can be defined as a dimensional change occur when
the pressure from forming tool has been set free. Hambli & Kobi (2002) said after
bending, springback occurs simultaneously with the tool removal. The total of the
elastic recovery relies on the modulus of elasticity, E of the material and the level of
stress. The diversity of the thickness of the sheet metal after bending process and
mechanical properties of the material shows the problems faced concerning the
calculation to gain the prediction of the springback of the bent part and required
punch displacement. This lead to the bend angle arc repeatedly not accurate enough
to fulfil today’s requirement of high tolerance. To enhance the air bending process
accuracy, the variety of material properties at the time and after bending process
should be foresee especially the damage contour in the sheet. The paper explains an
L-bending in the finite element model to predict the springback elasticity. While
Suchy (1998) defined springback as a total of elastic distortion a material has to
7
undergo before it is deformed permanently, or formed. The total of elastic tolerance,
which is exist almost in every material, even if it is a ductile, hard-strength maraging
steel or an annealed metal. In ductile materials, the springback is much lessened
compare to the hard metals, based on the Young modulus (also called as modulus of
elasticity) of a certain material. High yield strength or the material’s strain-hardening
tendency resulting increase greatly the amount of springback. The amount of
springback in the material can be increased by using a heat treatment and cold
treatment. By comparing the low-strength steel material spring back, it will be
smaller compared to the high-strength steel and yet the aluminium’s springback will
be higher to two or three times higher. Springback happens in all types of bent-up or
formed parts when punch withdrawal and a forming pressure is released. The
material with predetermined placement influenced by two elements and the outside
restrictions suddenly removed and instantly performs an attempt to restore its
original form and shape.
According to Altan & Tekkaya (2012) Springback is a usual phenomenon that leads
to a deviation of shape from desired design geometry and that happen after
deformation of elastic-plastic of the part during process of stamping, springback
escalate corresponded with the magnitude of the flow stress, which is local strains,
and it's decline corresponded with the magnitude of the geometric restrain produced
from the shape of the formed part. After the forming load is removed, or when the
part is cut back, the elastic stress exists in various places on the part are released. The
part’s geometry, however, prevent all the strains to equal to zero. Thus, springs back
only partially or the part is relaxed, while remaining residual stress left in the part
after the spring occur. While Demeri (2013) stated that Springback is the shift of the
shape from that of the part after the die is released and after the forming occurred.
Therefore, it is a final product form’s deviation from the desired shape. Springback
arises during operations of drawing because they consists of drawing and stretching
components. The both components are accountable for springback. During bending
the outmost surface of the bent sheet is in tension condition, while, the inner surface
is in compressed condition. As the bending process develops, at the centre of the
cross section of sheet metal, the neutral axis moves toward the direction of the inner
surface (compression side). After the load is released, elastic recovery leads to the
8
springback. However, in stretching forming, practically the springback is negligible
because the tensile deformation in both the inner and outer surfaces of the sheet
thickness.
2.3 Springback effect and Thinning Effect on various thickness
One of the parameter of the springback effect which is thickness of the material.
According to Davis (2004) geometrical factors enormously influenced the
springback, and ratio of bend radius and bend angle to thickness of sheet increase.
Dixit, Narayanan, & Ganesh (2013) said that the results related to the effect of
caused by the another parameters such as Young’s modulus and the thickness of the
sheet were expected. The radius of the punch nose and the sheet thickness was
proved to have a noticeable effect on springback. The texture of the surface is spoilt
caused by the orange peeling which is the common problem in bent parts. A size of
coarse grain is relative to the thickness of sheet (a high d/t ratio) is established fact to
bring this defect. The sheet thickness, initial grain size, rate of roughening, true
strain, and initial surface roughness define the roughness of the surface. The effect of
initial surface roughness and grain size for a sheet thickness with 1.27mm is deem to
be significant. Substantial roughening resulted from an addition of the size of grain
within range of 50 pm to 200 pm., while a initial surface roughness with a wide
range done a little effect. According to Lemeš (2010) said the strain change caused
by the elastic recovery is one of the parameter of springback. The other factors that
will increase the springback is The strength of the material is higher, the radius of the
die is larger, lower Young’s modulus, and higher wipe steel clearance. Advanced
materials for example, high-strength steels and aluminium alloys have a higher
tendency to display greater springback.
Gassara et al (2009) stated a case is presented to optimize three parameters which is
the punch of the die, die clearance, the blank holder force and the radius of the die
corner. While Kitayama, Huang, & Yamazaki (2012) mentioned there are a lot of
factors affecting the springback, for example, the blank holder force (BHF), material
properties, lubrication conditions of the interface and friction, number of integration
9
points, die geometry, punch speed and so on. For Yeh, Li, & Tsay (2012), the
springback primarily affected by the metal sheet’s thickness, radius of die profile,
punch radius, and material parameters. According to Fu & Chan (2014) declared it is
disclosed that the sprignback increase when punch-die clearance, die angle, and die
radius increase. In addition, it is showed that the strip along the rolling direction
displays a bigger springback than that of the transverse direction.
Gassara et al (2009) In L-bending process, the final shape of the workpiece is greatly
influenced by the springback after the punch is removed. Since all materials have
their own a finite modulus of elasticity, when the load/punch is removed, plastic
deformation is followed by some elastic recovery. This phenomenon named
springback (Figure 2.1).
Fig.ure 2.1: Process steps during bending and springback (Gassara et al, 2009)
2.4 How to Optimize Springback Effect and Thinning Effect
Lemeš (2010) wrote to preclude or lessen the springback, a lot of methods is applied
nowadays. The methods involve to prevent or reduce the springback is condering the
design of the die, which may go through 3-10 expensive try and errors before a
satisfactory geometry is acquired. Research on springback has been fixated to two
major issues which is to efficaciously predict springback and to counterbalance the
springback in tooling design. Numerical simulation of springback in complex auto-
body panels need a lot of operation for example deep drawing and binder wrap, is
use a lot of time and accumulated errors from each operation will impact negatively
to the accuracy of the simulation. While according to Dilip Kumar et. al. (2014), to
minimize the effect by the springback, several ways are used. The comprehensive
10
compensation (CC) method regard about the fact of displacement and large rotation
would happen during the springback, which is more familiar for panel stamping in
automotive industrial. While the second method is displacement adjustment (DA)
method which compensation of magnitude and direction are the two essential
aspects, has been proven successful in practice. However, theory about DA is not
present, tests in industrial show that the capability of this method relys on various
parameters as well as process settings, part geometry, and material.
Fu & Chan (2014) stated Liu et al. (2010) carried out the three point bending tests
using the copper foils to research interactive effect of specimen and grain sizes. It is
found that the springback increases with the decreasing ratio of specimen thickness
to grain size.. The similar result obtained by using brass foils is also reported by Gau
et al. investigated the size effect on the springback based on L-bending using
different size-scaled pure copper foils with similar microstructure. It is found that the
springback decreases with foil thickness when the influence of surface grain
dominates. When the foil thickness is decreased to a certain value, the strain gradient
effect takes place and the amount of springback increases with the decrease of foil
thickness.” While Demeri (2013) stated that “The key to removing springback is to
change the state of stress on the outside and inside surfaces of the sheet metal from
tension/comprcssion to tension/tension. This is usually done by superimposing a
small stretch at the end of the forming cycle.”
According to Suchy (1998) “There are several methods of springback removal in
bending, most of them utilizing either overbending or coining. In Figure 2.2, the
formed part’s sides are secured in their location after forming by a punch or die
section, which most often coins the material.
11
Figure 2.2: Methods of springback control in bending (Suchy, 1998)
Figure 2.3: Gap between forming punch and die (Suchy, 1998)
The bending method counts on the die’s curved bottom to return the formed part to
its flat position on retrieval of the bending forces. This will also force the sides
toward the center, eliminating the springback effect. In Figure 2.3 shown previously,
a method utilizing ironing action against the bent up sides of the part is depicted.”
12
According to conclusion by Panthi et al. (2010) “The following conclusions emerge
from this study:
1. Springback highly depends on material properties (yield stress, Young’s
modulus, strain hardening) and geometric parameters (thickness of sheet, die
radius, sector angle) at minimal load condition and it decreases with increase
in compression depth. It shows that near net shape can be achieved by proper
controlling the forming load. It is observed that any combination of material
and geometry becomes irrelevant after a certain forming load/compression
depth.
2. Springback increases with increase in sector angle.
3. Friction has negligible effect on springback.
4. The springback increases with increase in yield stress, strain hardening but it
decreases with increase in Young’s modulus.
While Altan & Tekkaya (2012) stated that the way to reduce the springback effect is
“Compensation for Springback. Springback can be compensated for by changing the
die sur-face (overbending/overforming), locally deforming (bottoming), or stretching
by a high restraining force at the binder drawbead. These springback compensation
procedures are classified as geometry-based compensation, which involves change in
the tool geometry, and mechanics-based compensation. Which compensates/reduces
springback by controlling the factors affecting forming mechanism and springback.
Figure 2.4: Schematic of overbending to compensate for spring back in bending
(Altan & Tekkaya, 2012)
13
top related